Eccentric winding alternating current dynamoelectric machine



Nov. 24, 1964 w. J. MORRILL ECCENTRIC WINDING ALTERNATING CURRENTDYNAMOELECTRIC MACHINE Original Filed March v, 1958 2 Sheets-Sheet lMIJUW. 0L1

INVENTOR.

WAYNE J. MORBILL ATTORNEYS Nov. 24, 1964 w. J. MORRILL 3,158,769

ECCENTRIC WINDING ALTERNATING CURRENT DYNAMOELECTRIC MACHINE OriginalFiled March 7/ 1958 2 Sheets-Sheet 2 INVENTOR.

WAYNE J.MORRILL .WMZ, MM

United States Patent 3,158,769 ECCIENTKUQ WENDRNG ALTERNATENG QURRENTDYNAIV'L QELEQTMC MAQHHNE Wayne 3i. Merritt, Electric Motors Speeiaities inc, Garrett, ind. Qontinuation of application No. 719,827,Mar. 7, W58. This application E an. ti, 1%2, tier. No. fddfififi li'i'(Claims. {@l. dllil i iill The invention relates in general toalternating current machines and more particularly to single phaseshaded pole fractional horsepower motors.

Shaded pole motors of the induction, reluctance and hysteresis types areused on small sizes where efficiency of operation is not a primeconsideration and where their cheapness of construction is a primerequisite. The simplicity and economies in construction of shaded polemotors would be utilized in larger sizes if the efficiency could beincreased.

Accordingly, an object of the present invention is to increase theefiiciency of shaded pole motors.

Another object of the invention is to provide a. single phase inductionmotor with a more nearly sinusoidal stator flux distribution.

Another object of the invention is to provide a shaded pole inductionmotor with a lower magnetizing currer and, hence, a lower wattage inputto the motor for the same wattage output.

Another object of the invention is to provide a shaded pole inductionmotor which has reduced odd harmonics in the flux distribution wave witha consequent reduction of the tendency of the motor to run at a reducedspeed and, therefore, a lower resistance squirrel-cage rotor may beused. With this lower resistance rotor, lower losses are incurred for agreater efiiciency.

Still another object of the invention is to provide separate windings ofdifferent pitches and other than concentric on a shaded pole inductionmotor.

Still another object of the invention is to provide a differentefi'ective magnetomotive force in the leading edge of the pole face thanon the central or main portion of the pole face.

The vast majority of shaded pole alternating current motors have been ofthe salient pole type. The use of the salient pole construction causesthe introduction in the stator fiux wave of large odd harmon cs of spacedistribution, mainly, the third, fifth and seventh harmonics. Theseharmonics act on the rotorto cause torques corresponding to those inmotors having three, five and seven times the fundamental number ofpoles. These harmonic torques, together with the load torque, can causethe rotor to stick at some low speed in which case the motor ever comesup to full operating speed; this tendency is commonly referred to as aharmonic dip. The bad effects of harmonic dips have been minimized inthe past by the use of a relatively high resistance rotor at thesacrifice of motor output and efiiciency. What this invention reallyaccomplishes is the substantial elimination from the stator flux wave ofthese large odd harmonics and thus elimination of the detrimental torquedips. This in turn permits the use of a much lower resistance rotor thanhas been heretofore possible with consequent improvement in motor outputand eificiency. Reduction of the odd harmonic stator fluxes furtherimproves the motor electrically by reducing harmful airgap reactancesand saturation effects in the magnetic paths pro duced by the harmonicfluxes.

Other objects and a fuller understanding of this invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

ice

FlGURE 1 is a plan of a single phase induction motor stator embodyingthe invention;

FEGURE 2 shows a modified form of the invention;

FiGURE 3 is a graph of performance curves;

FIGURE 4 is another graph of performance curves of the invention;

FIGURES 59 show flux distribution patterns useful in explaining theinvention; and

FIGURE shows a further modification of the invention.

FIGURE 1 shows a plan view of a shaded pole induction motor lll with theinvention applied thereto as an example, but not limitation. The motor11 has been shown as a four-pole motor but it may be of any number ofpoles. The motor if has a stator 12 and a rotor shown at 13. The rotorfor simplicity may be a squirrel cage rotor and has been found to beefficiently operable with copper conductors for a low resistance rotor.

The stator 12 has a magnetically permeable yoke 14 connectingmagnetically one end of a plurality of pole pieces 15. The other end ofthese pole pieces, which have been shown as being identical, terminatesin a pole face iii. With reference to only one of the pole pieces 15,the pole piece has first and second portions w and 24 A first slot 23extends into the first portion 19 and divides this first portion intofirst and second sections 2d and 25. This slot 23 extends away from theair gap 2-6 between the stator 12 and the rotor 13. The first section 24has a first pole face portion 27 and the second section has a secondpole face portion 28. A second slot 32 is defined by the space betweenthe first and second portions 19 and 2d and extends from the air gap 26to the yoke 14. The second portion 20 has a third pole face portion 33.A common slot 3% or winding space lies between each of the pole pieces15.

A conventional short circuited shading coil 35 is disposed in the firstslot 23 land encircles the first section 24 to act on the first poleface portion 27, which may be considered as a shaded pole face. Thefirst section 24 may thus be considered a shaded section.

The primary winding on the stator 12 is provided on each of the polepieces 15 but in order to simplify the drawing a winding is shown ononly one of the pole pieces 15. The primary winding includes a firstcoil or winding 38 encircling the entire pole piece 15', that is, bothportions 19 and 2t and it thus acts on and energizes the entire polepiece 15. This winding 38 has been shown for diagrammatic reasons asbeing of only a few turns, but it will be understood that in accordancewith usual practice, many turns are used. A second coil or winding 39encircles only portion 19 which is approximately threefourths of thepole piece 15 and accomplishes this by having a common coil side 40 inthe common slot 34 with the first coil 38, and also passes through thesecond slot 32 which thus provides a winding space. The windings '33 and39 maybe connected in series, as shown, for error-- gization from anexternal source. The shading coil 35 also has a coil side in the commonslot 34 coincident with the common coil side it) of the first and secondcoils 38 and 39. The trailing edge 41 of the pole face 16 is at the edgeof the shaded pole face portion 2'7 of section 24 where portion 27 meetscommon slot 34. The leading edge 42 of the pole face 16 is at the edgeof the pole face portion 33 of portion 20 where portion 33 meets commonslot 34 of the next adjacent pole piece configuration.

The shading coil 2'15, together with the first and second coils 38 and39, may be considered to be third winding means which provides a laggingfiux component in the first pole section 24 and consequently in thefirst pole face portion 27. This is in accordance with the usual shadedpole induction motor operating principles. Since the short circuitedshading coil 35 is in essence a short circuited secondary winding of atransformer, windings 38 and 39 being the primary winding, the currentswhich are generated by the secondary flux are in such a direction tooppose the primary flux and thus reduce its magnitude. .Thus, inaddition to producing a lagging fiux, the shading coil 35 also actstodemagnetize or reduce the in-phase flux. This reduces the flux of thepreviously rectangular corner C shown in dotted lines of the primaryflux distribution wave 43 shown in FIGURE to the value shown in solidlines, thus making the in-phase primary and shaded flux distributionwave have an approximately symmetrical shape as shown in solid lines,with beneficial results which will be hereinafter described. The corner44 of the wave 43 is reduced because of the lesser energization on thepole portion ill. The FIGURE 5 shows the wave 43 formed by the unshadedflux density B at the mid-portion, by the reduced magnitude fiux densityB at the leading portion of the pole face, and by the shade flux densityB at the shaded pole face portion 27.

In prior conventional shaded pole motors with uniform air gaps, the fluxwave produced peripherally in the air gap by the action of the fullpitch primary winding alone and Without the shading coil would have thefull rectangular wave form 49 shown dotted and solid in FIGURE 6,assuming slot openings to be of negligible width. The action of theshading coil in addition to producing a quadrature, in time, or laggingflux component in the shaded region also served to reduce the amplitudeof the shaded region in-phase, in time, flux to produce an in-phasestator flux distribution as shown in solid lines in FIGURE 6. Thedistribution wave of FIGURE 6 is plotted to show in solid lines theunshaded flux density B and that portion of the shaded flux density Bwhich is in time phase with B. It can be thought of as being the fluxdistribution in the stator at the time B is maximum. The quadrature orlagging (in time) flux component B produced in the shaded region is asshown in FIGURE 7.

The quadrature flux of FIGURE 7 is responsible for the ability of theshaded pole motor to start and it serves to improve the output andefliciency during running by adding to the fundamental forward rotatingfield and subtracting from the fundamental backward rotating field.

A very important effect or" the shading coil is that of demagnetizingthe shaded corner of the in phase flux wave 49 of FIGURE 6 to produce amuch better inphase wave form than would exist without the shading coil.This improvement in the in-phase wave form was the principal reason forthe surprisin ly excellent performance, compared to what might have beencasually expected, of the conventional shaded pole motor. motor of fullpitch primary coil construction which would not even continue to runwhen driven to full speed would not only start, but run quite well oncethe shading coil was added.

The surprise of early shaded pole motor engineers at the relatively goodperformance of their simple structures probably resulted from theirfailure to evaluate the benefits of the demagnetizing action of theshading coil. The reasons for the benefit are disclosed by modern theoryin accordance with which the only portion of the flux wave of FIGURE 6which can develop useful torque with the rotor at full speed is thefundamental sinusoidal component.

Any rectangular wave form, such as the rectangular flux wave asrepresented by the solid rectangular curve 49 of FIGURE 6 (including thedotted portion) consists of a fundamental sinusoidal component,represented here by the sine wave 5%, and an infinite number ofprogressively higher order sinusoidal odd harmonics. If the oddharmonics were completely absent, the flux wave 49 would conform exactlyto the shape of its fundamental sine wave 50. The deviations thereforebetween the rectangular wave 49 and the sine wave 50 are caused by theodd harmonics. It is these odd harmonics of stator flux which cause theaforementioned torque dips. The more nearly the rectangular fiux Wave 49can be modified to make it approximate the sine wave 5b, the less willbe the magnitude of the odd harmonics and their detrimental effects. Itwill be seen in FIGURE 6 that the demagnetizing action of the shadingcoil produces a flux Wave form which is stepped on one side and whichthus conforms more closely to the sine wave 54 In my Patent 2,773,999,issued December 11, 1956, I showed that the best Way to lop off therectangular corner opposite the shaded portion was to chamfer the poletip to make that portion of the stator flux wave conform very closely tothe sine curve and almost completely eliminate the corner. The resultingwave 53 is shown in FIGURE 8.

While the chamfered pole tip produced an improved stator fluxdistribution like the solid stepped curve 53 shown in FIGURE 8 andgreatly reduced the motor torque dips and increased output andefliciency, it had the disadvantage that the chamfered pole tip produceda large air gap at that pole tip which caused larger than necessaryrotor currents to flow at the instant the forward flux reached thislarge gap, and to a lesser extent substantially all the time. Inaddition, the large gap amounted, in effect, to throwing away some ofthe stator excitation for which ampere turns had been spent.

In accordance with the present invention the unshaded pole tip fiux ismade to conform more closely to the fundamental sine Wave by reducingits excitation while maintaining a uniform air gap. The fluxdistribution wave 54 of FIGURE 9 results from the new construction, asshown in FIGURE 1, and it can be seen that the new construction producesa flux distribution wave closely approximating a sine wave withoutintroducing a large air gap.

It should be especially noticed that the new winding 3849 is not aconventional concentric winding, but it is a displaced or eccentricwinding wtih one side of the shading coil 35 and one side of eachprimary coil in the same slot to maintain full excitation on the shadedsection and thus full efi'ectiveness of the shading coil. Thedemagnetizing action of the shading coil is used to bring the resultantin-phase flux wave into approximate symmetry and into approximaeconformity with a sine wave.

As a result of the new construction saturation of the unshaded pole face33 is reduced, torque dips are almost eliminated, harmonic brakingtorques at full speed are greatly reduced and rotor magnetizing currentsare re duced. Further and surprisingly, the motor excitation can beeffectively increased for the same degree of saturation and as a result,the output and efliciency can be furthcr increased as compared with eventhe chamfered pole tip construction of my aforesaid Patent 2,773,999;due to the elimination of the objectionable harmonic fluxes, the totalflux in the iron paths of the motor is reduced with the same excitation,or for the same degree of saturation a higher excitation may beemployed.

The fact that the flux distribution is more nearly sinusoidal eliminatesmuch of the odd harmonics such as the third and fifth harmonics and thisgreatly reduces the tendency of the rotor to stick at a reduced speed.In some prior art devices, if the clips in the speedtorque curveoccurring at about one-third synchronous speed and caused by the thirdharmonics are severe enough, as shown in the curve 58 of FIGURE 4, themotor could, on certain load conditions, accelerate to about one-thirdsynchronous speed but then not have sufficient torque to accelerate toits normal running speed. By the present invention, these dips in thespeed-torque curve are greatly reduced, as shown in curve SI of FIGURE4, because of the more nearly sinusoidal fiux distribution, andtherefore, a lower resistance rotor may be used than is normally usedwith these small shaded pole induction motors. A substantial reductionin resistance is obtainable, such as by changing from aluminum to copperconductors of the same or larger size. The lower resistance rotorpermits even greater efiiciency by reducing the PR losses of the rotorfor a given wattage output.

The FIGURE 3 shows a speed-torque curve to" of a motor incorporating thepresent invention. This curve 45 may be compared with curves as and 4,7.Curve d? is that of anordinary prior art single phase shaded poleinduction motor of the same general stator dimensions; namely, the sameamount of iron and the same ampere turn input but, of course, with thestandard prior art form of pole piece. The curve 4 6 is a curve of thesame basic motor but with the leading edge of the pole face chamfered ortapered as shown in my Patent 2,773,999. This resulted in an improvementin torque and cfiiciency over the standard shaded pole motor as shown incurve 47. The curve 4 of the present invention is of a motor with thesame excitation as the motor for curves 46 and 57 and shows thesuperiority of the present invention over not only the prior artstandard form, but also my previous invention with the tapered pole tipas shown by curve as. Curve 4% is a speed-torque curve of the presentinvention with the primary windings over-excited by a one hundred fortyvolt supply as compared to the standard of one hundred fifteen volts onthe motor, resulting in curve 45. In the past it has not been foundpossible to over-excite the standard motor of curve 4-7 or the taperedair gap motor of curve 46 without causing a considerable saturation ofthe iron and seriously decreasing the efliciency. In the present case,there was very little saturation in the iron and the torque increasedconsiderably as shown by curve 48. The same performance of curve 43 maybe obtained at normal one hundred fifteen volt excitation by increasingthe wire size and decreasing the primary turns in a manner well lrnownto all motor engineers.

FIGURE 4 is a graph of the motor of the present invention and shows acurve 51 of speed versus torque and also shows a curve 52 of efficiencyversus torque with the efficiency rising to a maximum at a verydesirable region; namely, near the maximum torque operating condition.

The air gap at each of the pole face portions 27, 28 and 33 ispreferably equal, that is, the radial length of the gap across which theflux must travel between the rotor and stator is equal. The arcuateextent of the pole face portions is variable. However, preferably theextent of the first pole face portion 27 is about one-fourth of the poleface or pole pitch, or forty-five electrical degrees, and the secondpole face portion, which is the main or central section, is aboutone-half the entire pole face or about ninety electrical degrees. Thethird pole face portion 33 thus accounts for the remainder and, whilethis is normally about one-fourth of the pole face portion, it may stillbeneficially vary widely from this value.

FIGURE 2 is a modified form of the invention as applied to a pole piece55. In this case, the pole piece retains the first slot 23 and shadingcoil 35 but additionally second and third slots 56 and 57 are provided.These slots extend from the air gap toward the yoke 14. The first coil38 encircles the entire pole piece 55, a second coil 59 passes throughthe third slot 57, and a third coil 6t) passes through the second slot56. All three coils 38, 59 and 6d have a common coil side at at and allcoils on one pole piece 55 are connected in series.

The pole piece 55 of the modified form of the invention, while morecomplicated and more costly, is an electrical improvement over the polepiece of FIGURE 1 because the flux distribution wave has two stepstherein rather than only one step and, hence, the flux distribution waveis more nearly sinusoidal.

In the modification of FIGURE 2, the entire pole face again has a firstportion 27 and has a main portion 62. This main portion may be in theorder of forty percent of the entire pole face are. The third and fourthpole face ti portions 63 and 64-, as determined by the slots 56 and 57,are preferably about the same arcuate extent and total betweentwenty-five and forty percent of the entire arc of the pole face.

FIGURE 10 shows a further modification of the construction of FTGURE 2,wherein two shading coils 65 and are used, both having a coil side inthe same common slot or winding space as the coil sides 61. Thisconstruction maintains consistency of complication of the primarywinding and the shading coil winding. The shading coil 65 is in a slot67 and the shading coil 66 is in a slot 68. The slots 6'7 and 68 arepreferably about one-sixth and one-third, respectively, of the polepitch from the trailing edge at the common coil side dl. The resistancesof the two shading coils may be adjusted to bring the resultantiii-phase stepped wave as closely as possible into conformity with asine wave. Obviously, the use of more than one shading coil, whileincreasing the complication of the motor and its cost, would, ifproperly done, improve the iii-phase flux distribution curve over whatcould be obtained with one shading coil. The improvement in the in-phasewave form would, in many cases, result in improved motor performance,provided the additional stator slot openings do not introduce sufficientcounterbalacing reluctance effects.

This application is a continuation of my application Serial Number719,827 filed March 7, 1958 and now abandoned, which is acontinuation-in-part of my application Serial Number 706,138 now PatentNumber 3,08l,043 filed December 2, 1957.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to Withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. A pole piece for an alternating current motor, comprising, lirst,second, and third pole face portions disposed in that order on said polepiece, first and second energizing winding means energizable from anexternal source acting on said pole piece and establishing a firstmagnetomotive force at said second pole face portion and a secondmagnetomotive force of lesser magnitude at said third pole face portion,and third winding means establishing a magnetomotive force at said firstpole face portion displaced in phase from said first magnetomotiveforce.

2. in an alterating current motor, a magnetic pole piece having first,second and third pole face portions, said second pole face portion beingintermediate said first and third pole face portions, first and secondwinding means acting on said pole piece for establishing a firstmagnetomotive force at said second pole face portion and a secondmagnetomotive force in phase with but of lesser magnitude than saidfirst magnetomotive force at said third pole face portion, and thirdwinding means cooperating with said first and second winding means forestablishing at said first pole face portion a third magnetornotiveforce phase displaced with respect to said first magnetomotive force.

3. An alternating current motor including a rotor and a pole piece,first and second portions of said pole piece, first and second pole faceportions on said first portion, said and second pole piece portionsdefining a slot extending into said pole piece, a third pole faceportion on said second pole piece portion, each said pole face portiondefining substantially equal air gaps with said rotor, first and secondwinding means on said pole piece at least partially in said slot andencompassing different extents of said pole piece to establish a greaterflux density at said second pole face portion than at said third poleface portion, and means establishing a phase displaced. component offlux in said first pole face portion.

arssgrca 4. A pole piece for a shaded pole motor, comprising, first andsecond portions of said pole piece, shading coil means on a section ofsaid first portion of said pole piece remote from said second portionand defining a shaded section of said pole piece, a shaded poie faceportion on said shaded section and a main pole face portion on theremainder of said first pole piece portion, a third pole face portion onsaidsecond pole piece portion, and first and second energizing windingmeans energizable from an external source at least partially energizingsaid pole piece and establishing greater efiective magnetomotive forceat said main pole face portion than at said third pole face portion.

, 5. A shaded pole motor, comprising, a rotor, a pole piece having firstand second portions, shading coil means on a, section of said firstportion of said pole piece to define a shaded section of said polepiece, a shaded pole face portion on said shaded section and a main poleface portion on the remainder of said first pole piece portion, a thirdpole face portion on said second pole piece portion, said main pole faceportion being intermediate said shaded and third pole face portions,each of said pole face portions defining substantially equal length airgaps with said rotor, first and second winding means energizing saidpole piece and establishing a first flux in the air gap at said mainpole face portion and a second fiux in the air gap at said third poleface portion and having a lower flux density than said first flux.

6. A shaded pole motor comprising a rotor, a pole piece defining an airgap with said rotor and having first and second portions, a first slotextending into said first portion and defining first and second polesections in said first portion of said pole piece, a short circuitedshading coil in said slot and encircling said first section of saidfirst portion of said pole piece, first and second pole face portions onsaid first and second pole sections, said first and second pole pieceportions defining a second slot extending into said pole piece, a thirdpole face portion on said second pole piece portion, each said pole faceportion defining substantially equal length air gaps with said rotor,first and second winding means at least partially energizing said polepiece and establishing a first flux in the air gap at said second poleface portion and a second flux in the air gap at said third pole faceportion of lower flux density than said first flux.

7. A single phase dynamoelectric machine including a pole piece having acentral portion and two side portions, first winding means energizingthe entire pole piece, second winding means cooperating with said firstwinding means and encircling at least said central portion to establisha magnetomotive force therein of greater magnitude than at one sideportion, and means establishing in one of said side portions amagnetomotive force which is phase displaced relative to themagnetomotive force in said central portion.

8. A single phase dynamoelectric machine including a pole piece having acentral portion and two side portions, first, second and third Windingmeans, said first winding means energizing the entire pole piece andhaving a coil side on one side of said pole piece, said second windingmeans energizable from an external source and encirciing said centralportion and one side portion and having one coil side on the same sideof said pole piece as said coil side of said first winding means, saidthird winding means including a short circuited coil acting on one sideportion of said pole piece and having a coil side on the same side ofsaid pole piece as said coil sides of said first and second windingmeans.

9. A shaded pole singlephase motor including a pole piece, first, secondand third winding means on said pole iece, said first winding meanshaving a coil side and encircling the entire pole piece, said secondWinding means energizable from an external source and encircling lessthan the entire pole piece and having one coil side in the same windingspace as said coil side of said first winding means, and said thirdwinding means including a short circuited coil having a coil side insaid winding space and encircling a portion of said pole piece differentfrom that encircled by said second winding means.

10. A single phase motor, comprising, a rotor, a stator including aslotted pole piece, first winding means encircling the entire pole pieceand having a coil side in one of said slots, second energizing windingmeans energizabie frornan external source and encircling less than theentire pole piece and having one coil side in said one slot, and thirdwinding means including a short circuited coil having a coil side insaid one slot and encompassing a portion of said pole piece differentfrom that encircled by either said first or second winding means.

11. A single phase shaded pole motor including a sioted pole piece,first, second, and third winding means on said pole piece, said firstwinding means energizing the entire pole piece, said first Winding meanshaving a coil side in one of said siots and establishing a firstmagnetomotive force in said pole piece, said second winding meansencircling approximately three-fourths of said pole piece, said secondwinding means having one coil side in said one slot and together withsaid first Winding means establishing a second magnetornotive force ofgreater magnitude than said first magnetomotive force in said polepiece, said third winding means including a short circuited coilencompassing approximately one-fourth of said pole piece and cooperatingwith said first and second winding means to establish magnetoinotiveforce in said pole piece which lags said first magnetomotive force.

12. A single phase shaded pole motor, comprising, a stator having aplurality of slotted pole pieces, first, second and third winding meanson each pole piece, each said first Winding means including a first coilencircling the entire respective pole piece and having a coil side inone of said slots, each of said second winding means including a secondenergizing coil energizable from an external source and encirclingapproximately three-fourths of the respective pole piece and having onecoil side in said one slot, each of said third winding means including ashort circuited coil encompassing approximately onefonrth of therespective pole pieces and having a coil side in said one slot.

13. A shaded pole induction motor, comprising, a plurality of pairs ofpole pieces, a yoke interconnecting one end of each pole piece, asquirrel cage rotor magneticaily cooperating across an air gap with theother end of each pole piece, each pole piece comprising first andsecond portions, first and second pole sections in each said firstportion of said poie piece defining a slot extending into each saidfirst portion from said air gap, a short circuited shading coil in eachsaid slot and encircling the respective first pole section, first andsecond pole face portions respectively on said first and second polesections, each said first and second pole piece portions defining asecond slot extending into said pole piece from said air gap, a thirdpole face portion on said second pole piece portion, each said pole faceportion defining substantially identical length of air gaps with saidrotor, a first winding entirely encircling each pole piece, a secondwinding connected in series with each first winding and encircling onlysaid first portion of the respective pole piece through the respectivesecond slot, said first, second and third pole face portions of eachpole piece subtending in the order of forty-five, ninety, and forty-fiveelectrical degrees, respectively, each of said first and second windingsestablishing a first flux in the respective second pole face portion anda second flux in the respective third pole face portion having a lowerflux density than said first flux.

14. A one and one-half coil per pole shaded pole induction motor,comprising, two pairs of pole pieces, a magnetic yok interconnecting oneend of each nole piece, a squirrel cage rotor magnetically cooperatingacross an air gap with the other end of each pole piece for a total offour distinct flux paths through said pole pieces, yoke and rotor, eachpole piece comprising first and second portions, first and second polesections in said first portion of said pole piece defining a first slotextending partially into said first portion from said air gap, a shortcircuited shading coil in each said slot and encircling the respectivefirst pole section to define a shaded section of the respective firstpole portion, first and second pole face portions on each said first andsecond pole sections, each said first and second pole piece portionsdefining a second slot extending from said air substantially to saidyoke, 21 third pole face portion on each said second pole piece portion,each said pole face portion defining substantially identical radiallengths of air gaps with said rotor, a first winding entirely encirclingeach pole piece, a second winding connected in series with each firstwinding and encircling only said first portion of the respective polepiece through the respective second slot and excluding said second polepiece portion, said first, second and third pole face portions of eachpole piece subtending in the order of forty-five, ninety, and forty-fiveelectrical degrees, respectively, each said first and second windingsestablishing a first fiux in the respective second pole face portion anda second flux in the respective third pole face portion in phase withand having a lower flux density than said first flux, each said shadingcoil cooperating with the respective first and second windings toestablish a third flux in the respective first pole face portion whichlags said first flux.

15. A pole piece for a shaded pole single phase induction motor having apole face on said pole piece and adapted to define an air gap with arotor, said pole piece comprising, first and second edges on said poleface, said pole piece having a first slot extending therein from saidpole face approximately one-fourth the pole pitch from said first edge,said pole piece having a second slot extending therein from said poleface approximately onefourth the pole pitch from said second edge,first, second and third pole face portions on said pole face with saidfirst portion being defined by the area between said first edge and saidfirst slot, said second pole face portion being defined by the areabetween saidfirst and second slots, and said third pole face portionbeing defined by the area between said second slot and said second edge,a shading coil lying in said first slot and de fining an annular ringaround that portion of said pole piece lying behind said first pole faceportion, a first stator winding circumscribing said pole piece, and asecond stator winding connected in series with said first Winding andcircuniscribing the section of said pole piece behind said first andsecond pole face portions, said first and second windings establishing afirst magnetomotive force in the portion of said pole piece lying behindsaid second pole face portion and a second magneto motive force in theportion of the said pole piece lying behind said third pole face portionin phase with be having lesser magnitude than said first niagnetoniotiveforce, and said shading coil cooperating with said first and secondwindings to establish in said portion of said pole piece lying behindsaid first pole face portion a third magnetornotive force having alesser magnitude than said first niagnetornotive force thereby toprovide a more nearly sinusoidal fiux distribution across said pole faceand in said air gap 16. A shaded pole single phase induction rnotor,comprising, a squirrel cage rotor and a stator cooperable therewith,said stator comprising an annular permeable yoke and an even pluralityof pole pieces, each said pole piece having a pole face defining an airgap with said rotor and having leading and trailing edges, each saidpole piece having a first slot extending therein from said pole faceapproximately one-fourth the pole pitch thereof from said trailing edge,each said pole piece having a second slot extending therein from saidpole face approximately onefourth the pole pitch thereof from saidleading edge, each said second slot extending into the respective polepiece to a point closely adjacent said yoke, first, second, and thirdportions on each said pole face with said first portion being defined bythe area between said trailing edge and said first slot, said secondpole face portion being defined by the area between said first andsecond slots, and said third pole face portion being defined by the areabetween said second slot and said leading edge, a shortcircuited shadingcoil lying in each said first slot and defining an annular ring aroundthat portion of the respective pole piece lying behind the respectivefirst pole face portion, a first stator winding coil entirelycircumscribing each pole piece, and a second stator winding coilconnected in series with each first coil and passing through therespective second slot and acting on only the respective first andsecond pole face portions, said first and second coils of each polepiece establishing a first flux in the respective second pole faceportion and the portion of said air gap defined thereby and a secondflux in the respective third pole face portion and the portion of saidair gap defined thereby in phase with but having a lower fiux densitythan said first flux, and each said shading coil cooperating with therespective first and second coils to establish a third flux in therespective first pole face portion and the portion of said air gapdefined thereby having a lower flux density than said first fiux therebyto provide a more nearly sinusoidal flux distribution across said poleface and in said air gap defined thereby.

17. A pole piece for an alternating current motor, comprising, incombination, first, second, third and fourth pole face portions on saidpole piece, first and second winding means acting on said pole piece andestablishing a first magnetoniotive force at said third pole face portion and a second niagnetomotive force of lesser magnitude at saidfourth pole face portion, and third and fourth winding means includingfirst and second short circuited windings acting on said first andsecond pole face portions, respectively.

References Cited in the file of this patent UNITED STATES PATENTS

1. A POLE PIECE FOR AN ALTERNATING CURRENT MOTOR, COMPRISING, FIRST, SECOND, AND THIRD POLE FACE PORTIONS DISPOSED IN THAT ORDER ON SAID POLE PIECE, FIRST AND SECOND ENERGIZING WINDING MEANS ENERGIZABLE FROM AN EXTERNAL SOURCE ACTING ON SAID POLE PIECE AND ESTABLISHING A FIRST MAGNETOMOTIVE FORCE AT SAID SECOND POLE FACE PORTION AND A SECOND MAGNETOMOTIVE FORCE OF LESSER MAGNITUDE AT SAID THIRD POLE FACE PORTION, AND THIRD WINDING MEANS ESTABLISHING A MAGNETOMOTIVE FORCE AT SAID FIRST POLE FACE PORTION DISPLACED IN PHASE FROM SAID FIRST MAGNETOMOTIVE FORCE. 